<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>04_计算器练习</title>
</head>
<body>
<input type="text" placeholder="请输入数字1" id="i1"> <br>
<input type="text" placeholder="请输入数字2" id="i2"> <br>
<button onclick="calc('+')">加</button>
<button onclick="calc('-')">减</button>
<button onclick="calc('*')">乘</button>
<button onclick="calc('/')">除</button>
<h4>运算结果:<span></span></h4>
<script>
    function calc(o){
        let n1 = document.getElementById('i1').value;
        let n2 = document.getElementById('i2').value;
        n1 = parseFloat(n1);
        n2 = parseFloat(n2);
        let spanE = document.querySelector('span');
        switch (o){
            case '+':
                spanE.innerHTML = n1 + n2;break;
            case '-':
                spanE.innerHTML = n1 - n2;break;
            case '*':
                spanE.innerHTML = n1 * n2;break;
            case '/':
                if(n2!=0){
                    spanE.innerHTML = n1 / n2;
                }else{
                    alert('除数不能为0!');
                }
        }
    }
</script>
</body>
</html>